Viscosity index improvers for lubricating oil compositions

摘要

Polymers suitable for use as a viscosity index improver for lubricating oil compositions including hydrogenated linear polymers characterized by the formula: D¹ - PA - Dº ;
and hydrogenated star polymers characterized by the formula: D¹ - PA - Dº n - X ;
wherein D' represents an "outer" block derived from diene having a number average molecular weight of from about 10,000 to about 120,000 daltons; PA represents a block derived from monoalkenyl arene having a number average molecular weight of from about 10,000 to about 50,000 daltons; D" represents an inner random derived from diene having a number average molecular weight of from about 5,000 to about 60,000 daltons; n represents the average number of arms per star polymer formed by the reaction of 2 or more moles of a polyalkenyl coupling agent per mole of arms; and X represents a nucleus of a polyalkenyl coupling agent.